Crushers are used to crush large aggregate particles (e.g., rocks) into smaller particles. FIGS. 1 and 2 illustrate one particular type of crusher, known as a cone crusher 12. In the illustrated cone crusher 12, large particles are fed to a feed distributor 14 (FIG. 2) where the particles are distributed into a feed hopper 16. Referring specifically to FIG. 2, the large particles fall into an annular space 18 between a bowl liner 20 and a mantle 22. The bowl liner 20 is secured to a bowl 24 which is threaded to an adjustment ring 26. The threaded interconnection allows the height of the bowl 24 to be adjusted relative to the adjustment ring 26, thereby accommodating a range of particle sizes. Hydraulic lock posts 28 can be used to selectively lock the adjustment ring 26 to the bowl 24.
The adjustment ring 26 is clamped to, but can move vertically relative to, a main frame 30, as described below in more detail. Alignment pins 31 maintain the adjustment ring 26 in alignment with the main frame 30. The mantle 22 is secured to a head 32 which is, in turn, secured to a main shaft 34. The main shaft 34 is eccentrically and rotatably mounted in a eccentric 36 which is, in turn, rotatably mounted in the main frame 30. The eccentric 36 is driven by a countershaft 38 through a pinion 40 that is secured to the countershaft 38 and a gear 42 that is secured to the eccentric 36.
Because of the eccentric mounting of the main shaft 34 (and associated head 32 and mantle 22) within the eccentric 36, the annular space 18 between the bowl liner 20 and the mantle 22 is not uniform. Rather, the space 18 varies about the circumference of the mantle so that the spacing includes a relatively large gap on one side of the mantle and a relatively small gap on the other side of the mantle. When the eccentric 36 is driven, the main shaft 34 (and associated head 32 and mantle 22) circumscribes an annular path (i.e., due to the eccentric mounting), thereby causing the large and small gaps to similarly travel in an annular path. This gyrating motion of the head 32 and the mantle 22 around the main axis of the cone crusher allows the feed material to enter the annular space 18. The material is then impacted and compressed between the mantle 22 and the bowl liner 20 in a series of steps as the material travels further down the annular space 18. The annular space 18 progressively gets smaller, thereby reducing the feed material down to the desired product size.
During crushing operations, it is not uncommon to encounter particles that are difficult to crush, sometimes referred to as "tramp." Small tramp will generally pass through the system without difficulty. However, sometimes even small tramp will become lodged between the mantle 22 and the bowl liner 20. In this situation, by virtue of the vertical movability of the adjustment ring 26, the bowl liner 20 will raise slightly to allow the small tramp to pass through the crusher. Such vertical movability of the adjustment ring 26 (and associated bowl 24 and bowl liner 20) is provided by a coil spring assembly 44 that clamps the adjustment ring 26 to the main frame 30.
In the illustrated crusher 12, the coil spring assembly 44 comprises sixteen coil spring subassemblies 46 circumferentially spaced around the main frame 30. Each coil spring subassembly 46 includes an upper frame flange 48 secured to the main frame 30, a lower spring segment 50, and five coil springs 52 between the upper frame flange 48 and the lower spring segment 50. Three spring bolts 54 extend through the lower spring segment 50, the upper frame flange 48, and the adjustment ring 26. Spring nuts 56 are secured to the lower end of each spring bolt 54. In the illustrated arrangement, the coil springs 52 bear against the underside of the upper frame flange 48, and push down on the lower spring segment 50, which in turn pulls down on the spring bolt 54 and nut 56 and associated adjustment ring 26.
The above-described arrangement affords upward movement of the adjustment ring 26 (and associate bowl 24 and bowl liner 20) against the force of the coil springs 52 in response to engagement of the bowl 24 and mantle 22 with tramp material, thereby allowing small tramp to pass through the system. It should be appreciated that, due to compression of the coil springs 52, any vertical movement of the adjustment ring 26 results in increased pressure being provided by the bowl liner 20 against the particles. The initial clamping force provided by the coil spring assembly 44 (i.e., before the adjustment ring 26 raises from the main frame 30) is on the order of about one million (1,000,000) pounds.
When large tramp particles become lodged in the annular space 18, the pressure created between the tramp, bowl liner 20 and mantle 22 can be so large that it causes the motor (not shown) driving the countershaft 38 to stall. In this situation, the tramp must be cleared by raising the adjustment ring 26 to a clear position, thereby increasing the annular space 18 to allow the tramp to fall or be pushed from the annular space 18.
To raise the adjustment ring 26 to a clear position, the illustrated crusher 12 includes four hydraulic actuators 58 (FIG. 1) that can be extended to push upward on the adjustment ring 26. The hydraulic actuators 58 must provide sufficient force not only to lift the weight of the adjustment ring 26, the bowl 24 and the bowl liner 20, but also to overcome the clamping force of the coil spring assembly 44, which force increases with compression of the springs 52. The force required to raise the adjustment ring can be on the order of about one and a half million (2,500,000) pounds or more. Such high forces require high hydraulic pressures which can lead to blown or leaking hoses.
In addition, there is a limit to the amount that the coil springs 52 can be compressed while raising the adjustment ring 26. This limit is due not only to the spring forces of the assembly that may exceed the maximum force that can be applied by the actuators 58, but also to the limits on compressibility of the coil springs 52 (i.e., the length of the fully compressed coil springs). As an example, the above-described crusher 12 is designed to raise the adjustment ring 26 only about two inches.